1. Field of the Invention
The present invention relates to a method and apparatus for image forming, a process cartridge and a toner, and more specifically relates to a method and apparatus for image forming capable of improving transferability and cleanability by supplying a lubricant, and a process cartridge for use in the apparatus, and a toner used in the image forming for obtaining an image having high thin line reproducibility.
2. Discussion of the Background
Recently, color image forming apparatuses using an electrophotographic methods have been in wide use. Digitized images are widely available, and printed images having higher image definitions are desired. Higher image resolution and gradients are studied, and toners visualizing electrostatic latent images having desired circularity and smaller particle diameters can be used to form images having higher definitions. A toner particle having a small particle size with a spherical shape is suitable for obtaining higher definition images. However, the toner having a small particle size with the spherical shape can easily slip through a gap between a cleaning blade provided in a cleaning unit and a photoconductive element, and onto a surface of a photoconductive element. Due to a spherical surface of the toner particle, the surface of the photoconductive element may not be cleaned, and the residual toner particles are scattered in the color image forming apparatus, thereby contaminating an image forming component such as a charging roller. As a result, a defective image having black dots and background fogging may be produced.
To eliminate the above-mentioned problem, an electrophotographic image forming method has been proposed. In the electrophotographic image forming method, a cleaning member is included for cleaning residual toner on a photoconductive element by using an elastic rubber blade after transferring a toner image onto a recording medium. Zinc stearate is incorporated in the toner by an amount from approximately 0.01% to approximately 0.5% with reference to toner weight, and the elastic rubber blade is substantially held on a contacting surface side of a cleaning blade on the photoconductive element by a supporting member for fixing the elastic rubber blade on the cleaning member.
However, when the zinc stearate is added to the toner, a layer of the toner including the zinc stearate applied on the surface of the toner becomes uneven depending on a condition of an image to be developed, and defective images can be produced.
Another cleaning unit has been proposed such that the cleaning unit includes a brush roller arranged in contact with an electrophotographic photoconductive element on the upstream side of the cleaning blade in the rotating direction of the electrophotographic photoconductive element, and that lubricant scraped from a stick-shaped molded element is applied on the surface of the photoconductive element.
The cleaning unit uses an electro-conductive brush to apply the lubricant onto the surface of the photoconductive element. However, the lubricant and the toner adhere on the surface of the electro-conductive brush, and the lubricant and the toner are difficult to remove from the surface of the conductive brush. Thus, a coating ability of the lubricant deteriorates.
Another technique has been proposed such that an image forming apparatus includes a cleaning blade which contacts a surface of a first image bearing member. A lubricant supplying unit provided in the image forming apparatus is disposed downstream from the cleaning blade in the rotating direction of the first image bearing member, and supplies the lubricant to the surface of the first image bearing member. A leveling-off unit also provided in the image forming apparatus is disposed downstream from the lubricant supplying unit in the rotating direction of the first image bearing member, and levels off the lubricant supplied onto the surface of the first image bearing member. However, the above-mentioned structure requires a relatively large and complex cleaning unit. This image forming apparatus uses a contact-type charging roller. Therefore, a leveled lubricant contacts the charging roller. The lubricant contacting the charging roller is conveyed to the surface of the charging roller, on which the lubricant adheres and accumulates. This varies a resistance value of the charging roller, and prevents a regular charging. The lubricant including fatty acid metallic salts such as zinc stearate can easily be attached to material such as nitrile rubber and urethane rubber that are generally included in a charging roller. Even when a surface of the charging roller is coated with fluorochemical coating material to prevent adhesion of foreign materials on the surface thereof, adherent lubricant are accumulated because the lubricant directly contacts the surface of the charging roller. On the contrary, the contact of the lubricant with the charging roller may substantially shorten a useful life of the charging roller.